forget the turbo, it's rings, on boost the pressure in the cylinders will stop oil being drawn into the bores, off boost the vac the pistons create will draw oil through into the cylinder, this is what is causing the problem.

oil leak in the turbo should be showing lots of oil in the exhaust housing and on boost would be far worse, check for thrust bearing damage, i.e. in and out movement of the shaft.

also pull turbo off and do general checks, if there is oil in the exhaust ports of the head, then it's rings, if there is oil in exhaust housing, then turbo.